1990 Audi 100 stumbling, hesistation

[Dennis Larson]

A few weeks ago I posted a message regarding stumbling and hesitation
on acceleration 1990 Audi 100 190,000 miles. The problem seems to be
a lean or inadequate fuel mixture.

Since that I received a number of suggestions, both on and off line
which were the same-

Change spark plugs and the fuel filter. The fuel filter seemed to
improve the overall power, the ignition was checking out ok and yes
the plugs were changed.

Making the rounds under the hood I found a loose vacuum hose, that
helped, but it was not *the* problem. I also found leakage at the
number 1,2,3 fuel injectors using propane gas. Upon removing the
intake manifold I found three injectors, the entire sleeves, loose
and working their way out of the holes with number one clearly out of
place. Seems the metal bar was not formed correctly to stop this from
happening.

I had purchased o-rings for the injectors, but not for the sleeves
the injectors are in. So I reinserted the cleaned injector assemblies
and gave it a coat of high-temp RTV on number 1,2,3 sleeves. The
injectors themselves were in the sleeves very tight so I left them
alone. The number 4 and 5 assemblies were also firmly in place so I
left them alone. The 1,2,3 injectors popped in neatly and I re-formed
the metal bar the so injectors are held in there firmly. I would have
bet my paycheck this was the problem.

Wrong.

The overall drivability is improving but the missing and lean
condition on acceleration is still there. But it is intermittent as
well. Stopping and going is fine, lots of power. Stopping and idling
means low power on start up and a mild miss on acceleration.

What I have accomplished so far is that with vacuum restored the
climate control now works fine, previously it didn't. Overall the car
is now drivable, previously it wasn't.

The problem is not constant, it is intermittent but it is there most
of the time.

I am now running out of ideas but some remaining ones- I could have a
bad injector(s) in there somewhere and I could still have a slight
vacuum leak as well. The car has 190,000 miles on it so injectors are
not out of the question. Since replacing these are pricey I will go
slow on this. The car does not exhibit any other problems common to
faulty injectors.

I have an ohm meter and the big Audi repair manual and am not finding
any faults so far.

Dennis

The original message-

I have a 1990 Audi 100 with about 190,000 miles on it that has had
deteriorating acceleration for several months. The car is used by my
wife for short trips, I use a 1985 Audi for myself. Last winter I
drove the car around for a day and the original power and zip came
back.

After driving it again after 6 weeks the car had gone downhill again,
worse than ever, so I added Techron and my more aggressive driving
habits for a day or two. It didn't help this time.

On startup the car is barely drivable and a long warm-up helps. It
acts like it is in a very lean condition with some mild backfiring in
the intake. So far I am investigating vacuum leaks. Pulling the dip-
stick out or removing the oil cap will stall the car out.

It idles perfectly, but accelerating and accelerating when in neutral
produces some mild missing. Flat and level driving is perfect.

I do have a vacuum problem with the climate control, the AC will
cycle from the dashboard vents to the bi-level position on
acceleration and the door locks are not functioning properly. But I
have not found any vacuum leaks yet for these problems.

Today I checked out the ignition wires and replaced one with higher
ohms 11k, but that did not improve the situation. I have some sensors
to check out, possibly a fuel filter (I am the third owner). I have
the full 3 volume repair manual on hand and am acquainted with
checking various sensors and their ohm values but some direction
would certainly help.